Method of continuously casting a uniform metal film

ABSTRACT

A weir assembly suitable for use in conjunction with a rotary table is described for use in producing flakes of solid material from solutions or from molten metal baths. In particular the novel weir assembly of the instant invention is described with reference to the preparation of sodium-lead alloys. The assembly of the invention includes a tank, baffled to provide for the smoothing out of waves which might form during the filling of the tank with molten alloy. The weir plate is provided with a notched top portion to provide a uniform sheet of molten material flowing down the face thereof. The molten metal is contacted with the cooling table surface off the surface of a spreading means positioned at the bottom of the plate.

United States Patent [72] Inventors Harmon A. McDougal;

Erwin C. Whitney, both of Beaumont, Tex. [21] Appl. No. 883,444 [22] Filed Dec. 9, 1969 [4S] Patented Aug. 17, 1971 [73] Assignee PPG Industries, Inc.

Pittsburgh, Pa.

[54] METHOD OF CONTINUOUSLY CASTING A UNIFORM METAL FILM 2 Claims, 2 Drawing Figs. [52] U.S. CI 164/87, 164/276, 164/281 [51] Int. Cl. 822d 11/06, B22d I H10 [50] Field of Search 164/87, 276, 28 l 82; 222/566; 6 Ill 8 [56] References Cited UNITED STATES PATENTS 1,291,603 H1919 Nagy 164/276 Primary Examiner-Robert D. Baldwin Atlorney-chisholm and Spencer ABSTRACT: A weir assembly suitable for use in conjunction with a rotary table is described for use in producing flakes of solid material from solutions or from molten metal baths. In particular the novel weir assembly of the instant invention is described with reference to the preparation of sodium-lead al loys. The assembly of the invention includes a tank, baffled to provide for the smoothing out ofwaves which might form during the filling of the tank with molten alloy. The weir plate is provided with a notched top portion to provide a uniform sheet of molten material flowing down the face thereof. The molten metal is contacted with the cooling table surface off the surface of a spreading means positioned at the bottom of the plate.

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HAEMON A.MF0ouoA1. fEw/A/ c. WHITNEY BY (M A m, A ORNE METHOD OF CONTINUOUSLY CASTING A UNIFORM METAL FILM BACKGROUNDOF THE INVENTION I Many methods have been described in the prior art for the preparation of flakes of material such as sodium-lead alloy, calcium chloride, caustic soda and the like. In instances where flakes of materials such as calcium chloride or caustic soda are produced, typically the operation involves the evaporation of water and the deposition of crystals of the desired salt or material on a moving surface. The solidified salt or hydroxide is subsequently flaked off the moving surface. In the preparation of metal alloys such as sodium-lead. alloy this flake preparation is accomplished typically by dipping a flaking wheel into a molten sodium-lead alloy bath.'The alloy to be solidified clings to the rotating surface of the wheel which is subjected to cooling. The cooling of the surface of the wheel causes solidification of the alloy on the wheel surface. The wheel is typically scraped during rotation to remove the solid metal from its surface.

Various alloys have been prepared in the past usingthis general type of flaking method. Thus, alloys of sodium-lead, lithium-sodium-lead, lithium-potassium-lead, lead-sodiummagnesium and other similar alloys of metals have been described in the literature. Typical literature describing such alloys and alloy preparation are U.S. Pat. Nos. 1,652,077; 2,061,267; 2,664,605 and 2,635,107.

While flaking methods using a typical prior art flaking wheel have been found to be effective in the preparation of sodiumlead alloys andother similar materials,they do suffer from certain drawbacks. First, the preparation of a metal alloy on a flaking wheel by rotating the wheel through amolten bath requires the maintenance of a substantial body of molten metal. .Therotation of the wheel in the molten bath causes agitation of the bath and uneven pickup of molten material sometimes results. In the case of solutions from which salts are being precipitated on the rotating wheel, the baths or salt solutions through which the wheel rotates are usually agitated to insure uniform distribution of salt throughout the solution.

With conventional flaking wheels considerable difficulty has been encountered even with the use of alloyedsurfaceson the wheels as described in U.S. Pat. No. 2,635,107 in removing a uniform deposit of sodium-lead alloy from a molten bath using rotary flaking wheels. This difficulty has resulted in theart having recourse to specially prepared surfaces on rotating wheels-such as shown in U.S. Pat. No.. 2,664,605. Despite these efforts nonuniformity still persists and in part is caused by rotation of the flaking wheel itself through a stationary bath and the resulting splashing that occurs.

THE PRESENT INVENTION In accordance with the instant invention a method of preparing flakes and in particular flakes of sodium-lead alloy is; provided which makes use of a novel weir assembly in conjunction with a flat, rotary table on which molten sodium-lead alloy may be deposited. The weir assembly is so constructed that a uniform thickness of alloy may be presented to the rotating table surface where it is cooled rapidly and removed from the table in an efficient manner. The method and apparatus of the instant invention involves the use of weir assembly that smooths the surface movement of the material contained in; the weir tank and presents to the notched upper surface of a weir plate an essentially smooth, even surface of liquid. ln the case of alloy preparation this liquid is molten alloy. Each notch of the weir plate is cut at the essentially same angle to provide for the discharge across the weir plate of even streams. of liquid or molten alloy. As these streams of liquid flow down the face of the weir plate, they merge one with the other to result in a. uniform film of material. This uniform film of molten material in the case of alloy preparation is presented tothe table surface from a spreader located at the end of the weir plate and the film of material is then cooled and flaked for-use.

For a more complete understanding of the instant invention, reference is made to the accompanying drawings in which:

FIG. 1 is an isometric view of a flaking assembly shown in a housing with the housing broken away to expose a flaking table, the weir assembly of the instant invention, and showing the flaking table in cross section to expose the internal circulation system used for the heat exchange fluid; and

FIG. 2 is a longitudinal section of FIG. 1 taken along line 11-11;

Turning to the drawings and with particular reference to FIG. 1, there is shown a housing or chamber 25 in which there is positioned the flaking table generally indicated by the numeral 11. Table I] has a flaking surface or top 15. Below the surface 15 is a chamber 6 formed by a plate member 17 and the sidewall 5 of the table II. A second chamber 4 is formed by plate member 18 and sidewall 5 of the table 11 and a third chamber 3 is formed by the bottom plate .16, plate 18 and sidewall 5. v 4 g As shown in the drawing (FIG. 1), table 1 l rotates with the rotation of shaft 12 and the top member 15 rides on collar 14 of the bushing 13. On the collar 14 there is shown an inlet 22 and an outlet 23 for the admission of heat exchange fluid and discharge of heat exchange fluid to and from chambers 3 and 4, respectively. Between chambers 3 and 6 fluid communication is established through a plurality of inlets or risers 19. A plurality of orifices 20 are provided in plate 17 and establish fluid communication between chambers 6 and 4.

Positioned above the table surface 15 and rigidly mounted or suspended from the roof 26 of housing .25 is a weir assembly. This assembly is composed of a pair of sidewalls 42 and 43, a back wall 44 and a front piece or weir 38. The bottom 44a of the weir assembly is shown in FIG. 2. The weir 38 is provided on its upper surface with a series of notches 39 from one side to the other. interposed between the weir 38 and back wall 44 is a baffle member 41 attached to sidewalls 42 and 43 and terminating in a vertical direction above the bottom 44a of the assembly (See FIG. 2).

The weir assembly is held in a fixed position above the table surface 15 by plates 53 and 52 which have clamped between them anchor plate 54. Anchor plate 54 is welded to the bottom of the adjustable support bolt 51 which is in threaded engagement with a threaded, recessed socket positioned in support member 32. A similar support member 33 with similar internal threads is provided above wall member 42. An adjustable bolt 59 is in threadedengagement with support member 33 on one end and is welded to a. plate 58 on the other extremity. Anchor plate 58 is held in place by a pin 57 mounted in the wall 42. Adjustment of the entire weir assembly up or down with respect to its spacing from the table surface 15 is readily accomplished by movement or rotation of the support members or hangers 32 and 33. Nuts 34 and 37 hold grease fittings 35 and 36 in place on the members 32 and 33', respectively.

. Grease fittings 35 and 36,are provided to prevent the male threads on bolts 51 and 59' from freezing in the female threads provided in elements 32 and 33 during operation, of the flaking table.

The unit is supported on the housing cover 26 by a suitable support plate 49' which is fixedly attached to the cover 26 by a plurality of bolts such as bolt 50. Two lifting lugs 47 and: 48 are provided in the plate 49 so that it may be easily lifted from its position on cover 26. An inlet 46 for the introduction of the material to beflaked is provided. In the drawing this is shown as alloy though materials other than alloys are contemplated. A pipe surrounds inlet 46. and houses heating elements (not shown) to maintain the alloy in pipe 46 molten.

Behind plate 49 is a second support plate 60 whichis affixed to cover 26 by a plurality of bolts such as bolt 61. This plate 60 supports a blade assembly which contains a blade member 68- shown in FIGS. I and 2 bolted to a support plate 72 by bolt 73 and rigidly fixed thereto with nut 74. Blade. support member Rod 77 is in threaded engagement with socket 82. This socket is sealed with a cap member 84. A nut 76 is fastened to the top of element 82 and holds a grease fitting 75. The grease fitting is set in a recess 88 in a plate 89 which is held in place by screw members 86 and 87.

Rod 77a is provided with a surrounding seal 64 which is mounted to the plate 60 by bolts 69 and 70. The upper end of the rod 77a is threaded and engages threads in cap 63 for firm attachment thereto. A nut 66a is provided which is attached to the upper end of rod 770 and the lower end of a rod 66. Rod 66 is attached to a cylinder 62 which is typically an air cylinder designed to apply constant pressure on rod 66 and consequently the knife assembly.

In the overall operation of the device and taking as exemplary its use in the preparation of sodium-lead alloy the flaking table and associated weir assembly is operated in the following manner.

Heat exchange fluid used in this instance was Mobil-Therm oil, a light motor oil stable at temperatures up to 500 F. It was pumped via chamber 7a in shaft 12 through openings 22 into the chamber 3. The table is rotated in the direction shown in FIG. 1. The fluid is pumped through chamber 3 and up through the risers 19 until chamber 6 is filled with the liquid. The fluid entering chamber 6 fills that chamber and emerges through orifices 20 as well as through the weephole 8 of FIG. 2. The discharged fluid from the weephole 8 enters chamber 7 of shaft 12 while the fluid passing across orifices 20 fills chamber 4 and exits into chamber 7 of shaft 12 via paths 23. The pressure drop across the chamber 6 and 3 at the orifices 20 is 5 p.s.i.g.

When circulation of heat exchange fluid has been established in the table the molten alloy is introduced via tube 46 and spout 45 to the interior of the vessel 38a. Baffle member 41 spaced from the bottom 44a of the vessel 38a smooths out the tendency of the molten alloy to ripple or form waves at the surface of the bath shown'so that a smooth surface of molten alloy is presented to the toothed openings or notches 39 cut in the top of the weir plate 38. The faces of the notches 39 cut in the top of weir plate 38 form a 90 angle with respect to each other. The slope of face plate 38 is at an angle of 15 from a vertical line drawn from the jointure of plate 38 and spreader 40. Molten alloy in the weir assembly passes through the notches 39 and flows by gravity down the face plate 38 and across the spreader 40 where it contacts the table top 15 passing underneath it in a counterclockwise path.-

The sodium-lead alloy is cooled by the fluid in chamber 6 which is in contact with the table surface as it rotates in the housing 25. An inert nitrogen atmosphere is maintained in the housing 25 during the flaking operation by maintaining a nitrogen pad on the system. This pad is provided by a 2-inch line not shown on the drawing but located in the back of the housing. The table is rotated at a rate of 10 revolutions per minute. As the table rotates, the alloy on the surface solidifies into a uniform sheet of solid alloy which ultimately in its rotation comes in contact with blade 68 ofthe blade assembly. This blade 68 is at an approximate l5 angle to the table surface and is firmly held in this relationship by the supports 77 and 7711. As the solid alloy passes in contact with the blade, it is broken off as shown in FIG. 2. The blade is angled in the manner of snow plow towards the outer edge of the table so that alloy as it is broken off by the blade is pushed off the outer edge of the table and falls into chute 28 seen in FIG. 1 to storage. Operating in this manner with a table 100 inches in diameter a product of solid sodium-lead alloy flakes is produced readily at levels on the order of 250 pounds per hour. The major pressure drop across the heat exchange system is the 5 p.s.i.g. across the orifices 20, the pressure drop across the remainder of the system being negligible.

While in the above description of the equipment certain dimensions, pressures and speeds have been enumerated, it will be obvious that considerable variation in these matters can be tolerated. Thus, table speed can be greater or less than enumerated above. Should it be increased, an increase inheat exchange fluid flow can be readily provided b ad'ustment of the flow in nozzle members 20 and inlets 1 T e pressure drop across nozzles 20 can be varied by varying the size of the orifice. This can be readily accomplished by providing replaceable nozzles in plate 17 or by replacement of plate 17 with another plate having different orifice sizes.

In the above example the weir plate notches 39 are described as forming an angle of 90 with respect to their faces. This angle of 90 forms the preferred embodiment of the invention. Some deviation from this angle is permissible and greater or less angles may thus be employed. In general these notches are cut such that the angle formed by the faces of a notch are between 60 to l20and preferably in the to l00range.

The angle that the face plate makes with respect to the vertical as described in the example is 15. This is the preferred embodiment and can be varied somewhat. Thus, an angle of between 10 to 30 may be used if desired. Preferably, how ever, this angle is maintained between 10 to 20. The spreading device 40 is cut at an angle with respect to the weir plate 38 such that it turns the falling film of molten alloy from the vertical direction it takes on the weir plate to a more horizontal component. This turning of the film in a more horizontal direction tends to lay it on the rotating table surface below the spreader uniformly and prevents any tendency to splash on contact if it were to fall directly on the table from the weir plate 38.

In discussing the invention with respect to the preparation of sodium-lead alloy a lubricating motor oil having some acidity and being stable at the temperatures encountered in this system (200 F. to about 400 is described as the heat exchange media. Obviously where other materials are being flaked a different coolant or heat exchange material will be employed. Thus, for a caustic soda flaking operation a chilled brine might be employed. The alloy is cooled during operation of the cooling system herein described from the molten temperatures to its solidification temperature typically 700 F. During its travel around the table the alloy is cooled typically to 300 F. or lower before it is scraped by the knife.

While the invention therefore has been described with reference to certain specific embodiments, it is not intended to be so limited except insofar as appears in the following claims.

We claim:

1. A method of depositing a uniform film of molten metal on a surface comprising filling a reservoir with the molten metal to be deposited, dividing the surface of the molten metal into at least two parts while permitting free communication of molten metal in the reservoir below the surface, providing a series of angular cuts in one wall of the reservoir to form a plurality of paths through which molten metal may flow, continuing the filling of the reservoir with molten metal to a level sutficient to cause the molten metal to flow through said paths, joining the plurality of molten metal streams so formed into a downwardly flowing unitary film of molten metal and depositing the molten metal film so formed on a continuously advancing surface cooled sufficiently to cause the molten metal to become solidified thereon.

2. A method of feeding molten alloy to a cooling zone comprising establishing a pool of molten alloy, dividing the surface of the pool into at least two parts while maintaining a unitary body of material below the surface of the pool, separating the surface of the pool of molten alloy into a plurality of small paths at one end of the pool, merging the plurality of small paths of molten alloy into a unitary sheet of molten alloy while flowing the said sheet of molten alloy down an inclined surface and changing the direction of flow of said sheet to a more horizontal direction prior to introducing the sheet to a substantially horizontal continuously advancing cooling surface for solidification thereon. 

1. A method of depositing a uniform film of molten metal on a surface comprising filling a reservoir with the molten metal to be deposited, dividing the surface of the molten metal into at least two parts while permitting free communication of molten metal in the reservoir below the surface, providing a series of angular cuts in one wall of the reservoir to form a plurality of paths through which molten metal may flow, continuing the filling of the reservoir with molten metal to a level sufficient to cause the molten metal to flow through said paths, joining the plurality of molten metal streams so formed into a downwardly flowing unitary film of molten metal and depositing the molten metal film so formed on a continuously advancing surface cooled sufficiently to cause the molten metal to become solidified thereon.
 2. A method of feeding molten alloy to a cooling zone comprising establishing a pool of molten alloy, dividing the surface of the pool into at least two parts while maintaining a unitary body of material below the surface of the pool, separating the surface of the pool of molten alloy into a plurality of small paths at one end of the pool, merging the plurality of small paths of molten alloy into a unitary sheet of molten alloy while flowing the said sheet of molten alloy down an inclined surface and changing the direction of flow of said sheet to a more horizontal direction prior to introducing the sheet to a substantially horizontal continuously advancing cooling surface for solidification thereon. 